If you hear a rattle in your bottle, it can be one of two things: either the weld (or a piece of it) that retains the integrity of the vacuum space has become dislodged and is now rattling in the space between the double wall insulation, or a small piece of metal called the “getter” has broken free and is now moving about freely at the base of your bottle. You can continue to use your bottle normally, it is still completely safe.
Both of these components have their respective functions within the internal walls of the bottle. A loose getter will not affect the insulation properties of the bottle whereas a broken weld or piece of it can potentially render the insulation useless because the vacuum seal can be compromised.
To check if the vacuum seal is still in tact, first ensure your bottle is completely empty and dry, then place you ear next to the opening and listen for a humming sound. If you can hear it, your seal is still intact!